Process of treating lead-zinc sulphide ores



Patented Nov. 314 11922.

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NIELS C. CHRISTENSEN, 0F SAUL LAKE GITY, UTAH.

PROCESS OF TREATING LEAD-ZINC SULPHIDE ORIIES. 7

mo Drawing. Original application filed October 13, 1919, Serial No.330,320. Divided and this application filed April 21, 1920. Serial No.375,492.

- galena ores described in my applications Se rial Nos. 327,400 and327,401 and the process of treating zinc sulphide ores described in myapplication Serial No. 327,402.

The process consists in treating the comminuted ore or concentrate witha hot concentrated chloride solution containing acid or ferric chloride,by which treatment thelead and silver from the lead and silver sulphidesare dissolved as chlorides, and the sulphur given off as H S or metallicsul phur as shown below:

The ferrous chloride formed by the reduction of the ferric chloride indissolvihg the lead and silver is readily regenerated as noted in themethod of precipitation later described.

The hot solution containing the lead and silver is filtered away fromthe zinc blende, pyrite and gangue material, and the silver ispreferably precipitated therefrom with metallic lead and the lead eitherby cooling or by electrolysis, or by a combination of both. The hotchloride solutions dissolve a much larger amount of lead chloride thanthe cold solutions, and the lead chloride may be separated from thechloride solution by taking advantage of thisfact.

Such a proportion of solution to ore may be used that a hot concentratedsolution of lead chloride is secured by the before described treatment.This solution is filtered away from the ore and then cooled and the leadchloride precipitated and separated from the cold solution. Theprecipitation of the lead by electrolysis is preferably used whendissolving solution contains ferric chloride, and the ferrous chloridethus formed is regenerated by the chlorine given off in theelectrolysis. tlon may be electrolyzed with an insoluble The chloridesolu-- anode in a cell with a diaphragm separating The precipitated leadchloride may also be melted and electrolyzed to secure lead bullion andchlorine. The chlorine thus secured is led into the ferrous solutionwhere it unites with the ferrous chloride to form ferric chloride thusregenerating the dissolving solution.

The hot acid chloride solution or the hot chloride solution containingferric chloride acts very rapidly on the galena and has comparativelylittle efiect on the blende due to the limited solubility of zincchloride in the chloride solutions. It is therefore possible to secure apractically complete extraction of the lead with but very little actionon the blende if a very little excess of acid or ferric chloride overthe amount necessary to bring the lead into solution is used. Thesolutions containing the ferric chloride are preferable in this respectto the acid solutions. As the chloride solution is used over and overagain in the process it very soon becomes saturated with the limitedquantity of zinc chloride which it will hold, and therefore acts butvery little upon the blende.

The residue from this lead treatment, if rich enough in zinc, may betreated by the ordinary roasting and zinc smelting methods, but in mostcases it will pay to treat this residue for the recovery of the zinc asoutlined below:

The residue from the lead treatment which contains the blende, pyrite,etc. and silicious gangue material, is treated with hot concentratedsulphuric acid which dissolves the zinc as a sulphate but has verylittle action on "the pyrite or chalcop rite. As noted in my patentapplication erial No. 327 ,402 the action of the hot acid upon theblende diflers with the strength of acid and the temperature. Thedissolving of the zinc should preferably be carried out with the acidsolution near its boiling point, and

' sufficient acid should be used to dissolve the The rapidity of theaction increases with the concentration of the' acid. The amount ofaction upon the pyrite also increases with the concentration of theacid. The iron sulphide combined with the zinc sulphide goes intosolution with the zinc as ferrous sul phate. As described in myapplication Serial No. 327,402 the hot sulphuric acids all holda muchlarger amount of zinc sulphate in solution than the-cold acid, the coldacids between and 95% holding practically the same amount. Theseparation of the zinc sulphate from the concentrated acid solution issecured by taking advantage of this difierence in solubility of the zincsulphate in the hot and cold acid. Such a proportion of acid to zinc inthe ore is used that a hot concentrated solution of zinc sulphateissecured. This pregnant solution is separated from'the'residue of oreand cooled, thus precipitating the zinc sulphate. The cold acid is thenre-heated and used for the treatment of more ore. As also noted in thisapplication the more concentrated the acid the larger the amount of zincthe hot acid will hold. It is therefore advantageous to use moreconcentrated acid in order to keep down the volume of acid used. Asbefore noted, however, the amount of iron which is brought into solutionfrom the pyrite or chalcopyrite also increases with the concentration ofthe acid, and as noted in my application Serial No. 327,402 the zincsulphate precipitated from the more concentrated acids is less readilyhandled than the precipitate from the more dilute solutions. Highertemperatures must also be used with the more concentrated acids tosecure the more the ore and the products desired. If the sphalerite ispractically free from combined iron, and it is desired to make a purezinc sulphate- 60% to acid would probably be used in order to avoid anyaction on the pyrite. If the blende contains con; siderable iron themore concentrated acids might be used since the zinc-sulphate would becontaminated with the ferrous sulphate from the iron in the blende, anda small additional amount of iron from the pyrite would not be soobjectionable as in the previous case.

The residue from the two foregoing treatments which contains pyrite,chalcopyrite and siliceous gangue material, is especially well suited tothe recovery of the sulphides therefrom by flotation, and a prac- Jtically complete recovery of these in a very clean concentrate isreadily made.

By the above treatments practically all the lead and the silver inthegalena may be recovered in very pure products, and most of the zincmay be recovered as a high grade zinc sulphate. Only a small amount ofzinc is brought into solution as a chloride in the lead treatment, andwhen acid chloride solutions are used this may be recovered byprecipitation with lime, though this precipitation would be morevaluable for cleaning the solution than for the zinc recovered. Thepyrite and chalcopyrite of the ore (with the gold, silver and copper .inthem) are also recovered in a high grade concentrate.

My process has given excellent results on complex ores which haveyielded to none of the ordinary methods of treatment, and is therefore avery valuable improvement in the treatment of lead-zinc sulphide ores,which has so long been an unsolved problem in metallurgy.

As it is obviously impossible to give the many minor variations oftreatment in the ractical application of my process to diferent oresunder different conditlons, I do not desire to be entirely limited bythe fore.-

going brief description but by the appended claims.

This application is a division of my application Serial No. 330,320,filed on or about October 13, 1919.

Having described my'process-what I claim and desire to patent is:

in treating the comminuted ore; with a hot acid concentratedChlOIldQSOllltlOD, thereby 1. The process of treating zinc'elead sul-'phide ores and concentrates, which consists dissolving the lead andsilver in the galena as chlorides, separating the pregnant chloridesolution from the residue of ore, and precipitating the lead therefromby electrolysis, treating the residue of ore from the fore oingtreatment with hot concentrated sulp uric acid, thereb dissolving thezinc as a. sulphate, separating the hot pregnantacid solution from theremainder of the ore, and cooling said solution and precipitating zincsulphate therefrom.

'2. The process of treating zinc-lead sulphide ores and concentrates,Which consists in treating the comminutedore With a hot concentratedchloride solution, containing ferric chloride, thereby dissolving thelead as a chloride, and reducing the ferric chloride to the ferrouscondition, separating the pregnant chloride solution from the remainderof the ore, and precipitating the lead therefrom by electrolysis, andusing the chlorine thus generated for changing the before mentionedferrous iron to the ferric condition, and using last said ferricsolution for the treatment of more ore, treating the residue of ore fromsaid foregoing treatment with hot concentrated sulphuric acid, therebydissolving the zinc as a sulphate, separating the hot pregnant solutionfrom the remainder of the ore, and cooling said solution, andprecipitating zinc sulphate therefrom.

In testimony whereof I have signed my name to this specification.

NIELS C. CHRISTENSEN.

